1. Field of the Invention
The present invention relates to an image-processing apparatus and method, a computer program, and a storage medium. More particularly, the present invention relates to image processing adapted to perform a background-color-removal process on an image.
2. Description of the Related Art
Generally, various image processes are performed in a copying operation of a digital color copying machine to faithfully reproduce an image of an original read by a scanner. Usually, most of sheets of paper on which the original is printed, that is, most of background color portions are not pure white in color and are slightly colored. Thus, in a case where the original is copied without modification, even the background color portion is faithfully reproduced using a color material. This phenomenon has various adverse effects, for example, an increase of waste of the color material.
A conventional method of eliminating the adverse effects has been known, in which the following optimal image processing is performed according to a color of the background color portion of an image of an original. That is, first, a luminance histogram (or a density histogram) of the image read by a scanner is generated. Subsequently, a signal level (hereunder referred to as a background color level) representing the background color portion of the image of the original is detected according to the histogram. Then, a process (hereunder referred to as a background-color-removal process) of removing the background color portion from the image of the original is performed by subtracting the background color level from a level of a signal representing the image of the original (see, for example, Japanese Patent Application Laid-Open No. 5-63968).
However, the foregoing conventional method has drawbacks in that when the background-color-removal process is performed, a signal value representing highlight data, which corresponds to a portion other than the background color portion, is changed, and in that, particularly, in a case where a printing unit of a copying machine performs spot color printing using light cyan and light magenta, a highlight portion, which should be printed in light cyan or light magenta, is removed by performing the background-color-removal process. Also, in a case where the background color level is set in a high luminance range, and where reproducibility of highlight data is prioritized, the foregoing conventional method has another drawback in that the removal of the background color portion is insufficient relative to the amount of a consumed color material.